Carbon footprint from a dairy farm with combined milk production and bioenergy systems

Milk production is a source of greenhouse gas emissions (GHG), which mostly consist of methane (CH4) from gastroenteric fermentation and from manure management. Implementing mitigation strategies, such as electricity generation from manure anaerobic digester (AD) and photovoltaic (PV) system contributes to mitigate manure CH4 emissions and fossil energy use for the dairy farm energy needs. This approach allows to consequently reduce the environmental impact of milk production. In the present study to evaluate this approach, a Life Cycle Assessment (LCA) was performed to analyze the carbon footprint (CF) of milk production in a dairy farm (1368 animals), provided by an AD and PV systems. “From cradle to farm gate” approach was chosen to detect the main environmental hotspots of milk production. The functional unit (FU) was referred to one kilogram of fat-and-protein-corrected-milk (FPCM). Beside milk product, other important co-products need to be considered are: meat and renewable energy production from AD and PV systems. AD plant was fed with a mix of manure and worse maize silage, not suitable for animal feed. IPCC’s tiered approach was adopted to associate a level of emission to each item in the life cycle inventory. A physical allocation was applied to attribute GHG emissions among milk and meat products. Renewable energy production from AD and PV systems were accounted discounting carbon credits due to the less CH4 manure emissions and to the minor exploitation of fossil energy. If mitigation options are not considered, CF of milk production was 1.36 kg CO2eq/kg FPCM. Considering the integrated dairy farm with bioenergy system, the mitigation resulted from milk production by 0.29 kg CO2eq/kg FPCM. AD had the highest reduction of GHG emissions, whereas PV system contribution in this case farm was negligible due to the small dimensions of the technology. The results obtained on this study show that integrating dairy farms with bioenergy systems (AD and PV) is one of the successful strategies to mitigate the environmental burden of milk production. The main benefit of this approach is the offset of fossil energy use and a more efficient manure management. In this case farm a preliminary approach was adopted, nevertheless exploring different domains such as technological, environmental and territorial features, social and economic ones, allows to achieve a more integrated LCA.